This invention relates to a system and method for venting air from a plurality of filaments with which the air has become associated. The air is used to cool the filaments in a filament quench chamber.
In the production of nonwoven fabrics, conventional melt-spinning techniques are employed at elevated temperatures to produce a plurality of melt-spun filaments, which are drawn by high velocity vent air systems. The hot filaments exit the spinneret and are openly drawn in a downward direction by the jet system. The filaments are simultaneously cooled and drawn in order to achieve the desired filament denier and strength properties. Therefore, nonwoven sheets produced from these filaments will have certain specified physical strength properties.
The cooling step conducted in the quench chamber employs a very stable, essentially laminar, air flow, which is typically introduced either parallel or perpendicular to the filament flow. A substantial air flow disturbance will result in problems such as weaving, sticking, entanglement, and breaking of the filaments. This is a particular problem in systems where large numbers of filaments are drawn by a single jet system.
As the filaments descend downwardly from the spinneret to the quench chamber exit, they are elongated by the draw forces imparted by the jet system and the speed of the filaments dramatically increase. The filament velocity within the quench chamber varies substantially from the upper end, where the hot filaments slowly exit from the spinneret, i.e., typically at less than about one foot per second (about 0.3 meter per second), to the lower end, where the filaments are traveling at generally about 200 feet per second (about 60 meters per second). Therefore, a filament velocity gradient is created within the quench chamber.
Each downwardly descending filament is surrounded by a boundary layer of air. This associated boundary air layer moves at essentially the same velocity as the filaments. Therefore, an air velocity gradient is also created.
Cooling air generally enters the quench chamber in a transverse direction, at the rate of about 1.5 to 7.0 feet per second (about 0.5 to 2.0 meters per second). Since the filaments are traveling at a relatively slow velocity as they exit the spinneret, the cooling air passes transversely through the filaments and can therefore exit from the upper end of the quench chamber. However, as the velocity of the filaments and associated boundary air increases to a rate in excess of the velocity of the cooling air, the cooling air becomes associated therewith, is carried to the lower end of the chamber, and exits therefrom with the filaments and the boundary layer air. Therefore, a "pumping effect" is imparted to the air in the quench chamber by the descending filaments. Any air surrounding the chamber which enters the quench chamber is also entrained and carried along with the downwardly descending filaments.
The conventional quench chamber and the air draw system, respectively, is open between the quench chamber exit and the jet draw system (see FIG. 1). The use of such devices results in impingement of the total pumped air stream described above on the jet draw system, causing turbulence, and disrupting the filament flow pattern.
Various types of systems are provided in the prior art, in which melt-spun filaments are quenched. In U.S. Pat. No. 2,982,994 to Fernstrom, for example, air from chamber 28 is introduced at the closed chamber 14. The air flow is introduced substantially concurrently with respect to the filament flow. The spent air is removed from passage 36 located at the top of chamber 14. In closing the intermediate area forming chamber 14, access to the filaments is unduly limited. Operations such as start-up and threading are particularly affected by this limited accessability.
U.S. Pat. No. 4,057,910 to Sachleben et al. describes a diffuser 1, in the form of a slatted cage, located within a closed quench stack 2, providing a means for facilitating exhausting of quenched air from quench chamber 2, in direction 9, while spun yarn 11 exits in direction 10. A closed, blast head device is also set forth in U.S. Pat. No. 3,946,546 to Venot for aspirating a textile thread with air.
Air transport systems have also been employed stabilizing the leading edge of a fibrous web (see U.S. Pat. No. 4,014,487 to Reba), for purposes of separating per se the air stream from the web, employing Coanda surface 44 and bar members 30. In this case, the web is not quenched with air.
In certain prior art systems, an enclosed intermediate area, such as described in the Fernstrom patent, will be satisfactory. For example, it would be quite acceptable for use in conventional textile spinning operations which employ take-up spools and winders.
However, they would be quite impractical for systems such as described in U.S. Pat. No. 3,692,618 to Dorschner; and U.S Ser. No. 192,973, filed Oct. 2,1980, now Pat. No. 4,322,027, to Reba, which employ high velocity air jet systems to draw the filaments as they exit from a spinneret. The use of these high velocity systems facilitates high filament draw-off speed, and relatively large numbers of closely spaced filaments are transported through the system on a continuous basis. At start-up of a system employing this filament draw apparatus, the entire spinneret output is typically advanced from a spinneret plate into a starter jet system located behind the primary filament draw system (see FIG. 1, starter jet system 80). This means that a path must be kept open from the spinneret plate to the starter jet system. Furthermore, a draw system of the type described above requires continuous monitoring of the filament count during operation to maintain a constant filament level with respect to the draw nozzle. If an access store door is provided in an enclosed system, such as the hinged door 22 of U.S. Pat. No. 2,982,994, and the door is left in an open position, turbulent air flow will be produced in the quench air chamber 14, causing a disruption of the filaments, as previously described.